A liquid supply apparatus is used to apply liquid such as photoresist solution to a surface such as for example semiconductor wafer and glass substrate for liquid crystal. The liquid supply apparatus includes a pump which causes a pump chamber to expand and contract. Japanese Patent No.: 3320896 discloses one example in which a pump chamber is separated by a bellows and a diaphragm. Japanese Patent No.: 4547368 discloses another example in which a pump chamber is separated by a flexible tube capable of elastic deformation. A pump referred to as “bellows pump” has a bellows serving as a pump member. A pump referred to as “diaphragm pump” has a diaphragm serving as a pump member. A pump referred to as “tube diaphragm pump” has a tube serving as a pump member. A pump referred to as “syringe pump” has a cylinder and a piston which reciprocates in the cylinder.
In each pump, an inflow-side check valve is disposed in an inflow-side channel between an inflow port of the pump chamber and a liquid container, and an outflow-side check valve is disposed on an outflow-side channel between an outflow port of the pump chamber and a liquid discharge member. The inflow-side check valve allows liquid to flow in a forward direction from the liquid container toward the pump chamber and prevents liquid from flowing in a backward direction. The outflow-side check valve allows liquid to flow in the forward direction from the pump chamber toward the liquid discharge member and prevents liquid from flowing in the backward direction. In this manner, each check valve is used to allow liquid to flow in the forward direction and to prevent liquid from flowing in the backward direction. As one example, a check valve to be incorporated in a housing containing a pump member is known, and as another example, a check valve to be coupled to a pipe connected to the housing is known.
In a check valve which is used in a liquid supply apparatus which supplies liquid to the discharge member, when pump operation stops, a valve element is moved downward by its own weight, comes in contact with a valve seat, and closes a valve hole. For example, in a liquid supply apparatus which supplies low viscosity liquid to the discharge member, when a pump operation is stopped, the valve element closes the valve hole in a relatively short time. On the other hand, in a liquid supply apparatus which supplies high viscosity liquid to the discharge member, after a pump operation is stopped, the valve element to be moved downward by its own weight takes a long time to come in contact with the valve seat and close the valve hole. For this reason, in the check valve incorporated in the liquid supply apparatus which supplies high viscosity liquid to the discharge member, a spring is required to apply a bias force directed toward the valve seat to the valve element.
When a photoresist solution is applied to a workpiece, the photoresist solution comes in contact with metal material, and the photoresist solution is deteriorated by metal material. For this reason, to prevent such a problem, Japanese Patent application Laid-Open Publication No.: 2003-127014 discloses that a spring made of fluorocarbon resin showing superior chemical resistance is used for the check valve.